Adjusting an outboard’s trim in or out is one of the most effective ways to improve a boat's overall performance. Trimming the outboard adjusts the boat’s attitude, or the angle of its bow into the water, which can help dial in the best ride by compensating for vessel load and sea conditions. In most cases, properly trimming also enhances fuel economy and top-end speed.
Experimenting with engine trim should be practiced in small steps until you acquire a solid, working feel for how your boat reacts to changes. From there, fine-tuning the ride through engine trim, throttle and trim tabs becomes second nature.
Here are some of the basics.
Trim for Results
When a boat is at idle, trim the outboard completely in, or down. This positions more of the lower unit into the water at a nearly vertical attitude, which provides unobstructed water flow to the prop. From this position, when you throttle up, the prop immediately "bites" and propels the boat onto plane. Threats of cavitation or "blowout" (where air and impeded water flow cause a prop to lose all bite and spin ineffectively) are virtually eliminated.
Once a boat is on plane and operating at a consistent speed, trim out to raise the outboard a bit. Doing so raises the bow and leaves less of the lower unit in the water, which reduces drag. Cruising speed picks up, and fuel economy improves as a result.
Based on the boat's attitude and ride, trimming out more can further improve performance. At wide-open throttle, trimming should yield higher rpm and top-end speeds. However, trimming out too far can degrade performance and cause the boat to porpoise, or bounce.
Trimming in lowers the outboard and allows more of the hull to settle into the water, particularly at the bow. This is advantageous when running directly into choppy water because it better positions the hull to slice through the water and allow a smoother ride. Again, dialing in the most comfortable ride comes down to acquiring a feel for your boat and how it reacts to engine trimming.
When entering a turn, trim the outboard in for maximum prop bite and handling, as well as superior planing capability when throttling out of the turn. Once you start to straighten out, begin trimming out the outboard and dialing in your most efficient cruising speed.
The Easy Way
Whether you’re new to boating or a seasoned veteran, you’ll appreciate the Mercury® Active Trim system, which takes the guesswork and effort out of properly trimming a boat. Active Trim is an integrated GPS speed-based automatic engine trim system that continually and instantly adjusts engine trim based on changes in boat speed and maneuvering.
Like when manually trimming a boat, the Active Trim system automatically trims out the outboard to its optimum cruising attitude and trims in when throttling back or entering a turn. The Active Trim system has five adjustable profiles that compensate for changes in weather, sea conditions, boat load and driver preferences. With one simple press of a button, the Active Trim system takes over. It can be overridden at any time by pressing the manual trim switch on the throttle.
The Active Trim system is compatible with most Mercury four-stroke outboards from 40hp and up, Mercury two-stroke outboards with SmartCraft® system capabilities, and SmartCraft-capable gas and diesel MerCruiser® sterndrive engines with digital trim senders.
Properly trimming the outboard is a critical step in achieving optimal engine performance. The Active Trim system makes it easier by taking the guesswork out of engine trimming.
Learn more about manual trimming and see the Active Trim system in action in this video from renowned saltwater angler George Poveromo, host of “George Poveromo’s World of Saltwater Angling” TV series.